A Sibling Comparison Study of Maternal Smoking During Pregnancy and Child Cognitive Functioning

Introduction: The current study examines if the links between maternal smoking during pregnancy (SDP) and child cognitive functioning withstand rigorous control for familial confounds. Methods: 173 families were recruited... [ view full abstract ]

Introduction: The current study examines if the links between maternal smoking during pregnancy (SDP) and child cognitive functioning withstand rigorous control for familial confounds.

Methods: 173 families were recruited based on birth record report in which mothers changed smoking behavior between two pregnancies. Assessments occurred when children were 7-16 years old. Mothers reported on their SDP (Todd et al., 2003). Parent and child inhibitory control (IC), set-shifting, verbal fluency (Delis et al., 2001) and auditory memory (AM; Wechsler, 1997; 2003) were assessed.

Statistical Approach: The sibling comparison approach involved fitting a series of hierarchical linear models. The standard models compared children whose mothers smoked (or smoked more) during pregnancy to those whose mothers did not smoke (or smoked less) for each outcome. The sibling comparison models assessed within- and between-family associations between SDP and each construct, allowing for a direct test of SDP effects.

Results: SDP was not associated with set-shifting or verbal fluency. Higher SDP severity was associated with worse IC and AM, suggesting a main effect of SDP. The AM—SDP association was robust to control for familial confounds, but the IC—SDP association was not. In the sibling comparison models, the within-family associations (child-specific SDP) were significant, suggesting potentially causal effects of SDP on IC and AM. The effect of SDP on AM, but not IC, was robust to control for genetic and environmental confounds. Approximately 75% of the variance in IC and AM was attributable to within-family differences. Thus, variability was primarily a function of differences between siblings rather than across families.

Discussion: These findings suggest that: 1) proximal environments may serve as effective targets of interventions seeking to improve children’s cognitive functioning in families with nicotine dependent mothers; and 2) underscore the need for genetically-informed studies of the effects of SDP on child outcomes.